It has been generally accepted that orthophthalic acid does not react with olefins having more than 5 carbon atoms. For example, in U.S. Pat. No. 2,975,210, this nonreactivity of phthalic acid toward olefins made it necessary to resort to preliminary formation of orthophthalic acid ester by reaction of orthophthalic anhydride and a primary alcohol, the orthophthalic acid ester then being reacted with olefin to give the desired ester. Such nonreactivity of orthophthalic acid with olefins was also the subject of an article in Industrial and Engineering Chemistry, Product Research and Development, Volume 2, dated 1963, at page 133.